Previous deafferentation experiments have been addressed to the task of determining whether somatic sensation, and sensory feedback in general, is necessary for various types of learning and for the performance of different categories of movement. Adult monkeys have been shown to be capable of making much greater use of limbs from which sensation has been abolished by dorsal rhizotomy than had previously been thought possible. The possibility remained, however, that sensory feedback may be required for the development of movement in ontogeny. Accordingly, to investigate the contribution of sensory feedback to the development of movement, one group of monkey neonates was subjected to forelimb deafferentation at birth and a second group of monkeys was both blinded and deafferented on the first day of life. To date, both groups of animals are capable of movement of their deafferented forelimbs, but their motor abilities have not been systematically assessed. The purpose of the proposed research is to define and to explore, by systematic testing and operant shaping procedures, the range and limits of precise movements and complex learning functions possible using the limbs deafferented at birth.